More than 50 Greater Boston theatre companies of all styles and sizes will unite onTuesday, September 10 in the Cyclorama at the Boston Center for the Arts (539 Tremont Street, Boston) for the first annual Greater Boston Theatre Expo. The public is invited to attend the free event held from 5:30pm to 7:30pm to meet representatives and artists from the region’s fringe, small, mid-sized, and large theatre companies, to get information about upcoming productions, and to take advantage of Expo-only ticket offers and giveaways.